The invention relates to a supporting plate for a denture model.
To manufacture dentures, e.g. crowns, bridges, inlays and the like, the dental technicien needs a positive model of the patient""s jaws and teeth. For that purpose the negative molds of the upper and lower jaw of the patient, supplied by the dentist, are filled with a mold material, e.g. plaster of paris, and covered with a supporting plate with retention pins extending into the mold material which remain in the mold material after hardening. After hardening of the mold material and removal of the negative mold a positive model of the patient""s upper or lower jaw is available on a supporting plate.
This positive denture model with its supporting plate is placed together with the respective counter jaw model of the patient into a jaw movement simulator (articulator) allowing to simulate individual jaw movements of the patient. This procedure allows to manufacture dentures exactly matching the patient""s own teeth and jaw positions and movements.
For the final modelling the denture model on the supporting plate has to be removed from and put back on the supporting plate. Very often the denture model has to be sawn into various jaw or tooth segments to make final modelling of this segment easier. For that pupose the denture model is detached together with the retention pins from the supporting plate and then sawn into individual segments.
After that the individual denture segments are put back on the supporting plate using the retention pins to place the segments as exactly as possible into their former position so that they are solidly secured on the supporting plate even in the case if the supporting plate is to be inserted into the upper part of an articulator with a row-of teeth of the denture model facing downwards.
According to the PCT Patent Specification WO 98/10709 a supporting plate for a denture model is given in which the side walls of the arc-shaped impression in the upper side have vertical grooves and where the bottom is to be equipped with a plurality of bore holes with inserted retention pins.
The retention pins are made of plastic and would be cut, too, when saw cuts are made in the denture model to obtain individual jaw or tooth segments, so that sawing becomes difficult, and partly sawn retention pins are remaining.
Another disadvantage of the known supporting plate is that all retention pins inserted in the bore holes in the bottom of the impression of the supporting plate become stuck in the hardened denture model and cannot be removed so that it becomes difficult to remove the denture model or individual jaw or tooth segments from the supporting plate or to put back the denture model or individual denture model segments on the supporting plate, the tilting of the retention pins in the bore holes and the angular position of the denture model or individual segments during removal or putting back leading to wearing out by friction or cracks of the mold material.
After hardening of the liquid mold material, e.g. plaster of paris, poured in the negative mold of a patient""s jaw and teeth and on which the supporting plate of the known design has been placed before hardening, the positive denture model removed from the impression in the supporting plated shows on its outer walls a ribbed structure corresponding to the grooves in the impression of the denture model so that the ribs in the outer wall of the denture model or of the segments mate the grooves in the side walls of the impression of the denture model when the denture model or the jaw and tooth segments are put back on the supporting plate.
However, the disadvantage is that the edges of the denture model or its denture model segments are considerably worn out by friction when the denture model is removed from the supporting plate and the denture model or individual denture model segments are put back or removed on repeated occasions.
The edges of the denture model, usually made of plaster of paris, are also worn out by friction or can chip off when a denture model segment is put back in the wrong place of the denture model in the impression of the supporting plate.
However, even the smallest damage on denture model and jaw or tooth segments, e.g. due to chipped-off edges or mold material worn out by friction will endanger the proper sitting of the denture model or segments on the supporting plate, so that the dentures manufactured according to the denture model will later on sit badly in the mouth of the patient.
The invention provides for the construction of a supporting plate for a denture model which makes it possible to repeatedly remove the denture model or individual jaw or tooth segments from the supporting plate and to exactly put back the denture model or individual denture model segments on the supporting plate without wearing out by friction the mold material.
This is achieved by means of a supporting plate for a denture model in which the height of the outer side wall of the arc-shaped impression on the supporting plate is considerably reducedxe2x80x94by approximately ⅘- and the outer side wall is vertical or slanted.
It is an advantage that the inner side wall of the arc shaped impression on the supporting plate has a stepped-shaped ridge at the level of the remaining opposed outer side wall of the arc-shaped impression, the ridge""s side wall is vertical or slanted, and the vertical or slanted side wall of the stepped-shaped ridge of the inner side wall and the outer side wall of the arc-shaped impression on the supporting plate have different contours along half of each length, the wall segments with different contours being opposite to each other.
It is useful that the vertical grooves of the remaining inner side wall above the step-shaped ridge are narrowing downwards.
In a different version of the invention the ribs between the vertical grooves narrowing downwards are widening downwards.
In another version of the invention the retention pins inserted in the bore holes are threaded at their upper ends extending into the arc-shaped impression on the supporting plate.
It is useful that the retention pins have a recess at their ends protruding from the lower side of the supporting plate.